The invention relates to a device for monitoring spatial areas with an emitter emitting radiation and a receiver receiving the emitted radiation, which is connected to an evaluation unit. The invention also relates to uses for the device.
Such devices are for example known as light curtains. Light curtains are used in numerous fields to safeguard hazard areas or to protect people or objects. They are an industrial mass-produced article. One typical application is personal protection in the working area of production equipment.
Essentially light curtains are a series of individual light barriers lined up along the entire monitoring area. A distinction is made here between passive and active variants. The active variants each comprise emitters with receivers opposite, while the passive variants comprise adjacent emitters and receivers, whereby the light emitted by the receivers is reflected back to the receivers by reflectors arranged opposite the emitters.
The known light curtains necessitate high assembly and method costs, as a plurality of individual light barriers has to be arranged along the entire monitoring area and housed in correspondingly large housings. Also the high level of susceptibility to failure of the known light curtains is disadvantageous. For example it is possible for incidental reflection from water surfaces to simulate the presence of people. Such failures occur principally in winter, when snow brought into buildings on people's shoes melts and forms small puddles. Also paper left in the monitoring area of the light curtains can cause incidental reflection and failure of the light curtains.
A device is also known from WO 99/34234 for recording a three-dimensional distance image. In the device for recording a three-dimensional distance image, light pulses are sent from an emitter towards an object to be measured, which are then reflected back to an optoelectronic CMOS sensor with a plurality of pixels with short-time integration. For a distance measurement a time measuring window is opened in the CMOS sensor, the duration of which corresponds to a predefinable integration time. The integration time is smaller than or equal to the length of the emitted light pulses. At the end of the integration time, the integration of the light pulses received by the pixels of the CMOS sensor is uniformly terminated. If the differences in reflectivity can be ignored, the charge assigned to each pixel of the CMOS sensor is a measure of the runtime of a light pulse assigned to the respective pixel. Recordings with different integration times allow the influence of reflectivity, which is different for different object points, to be eliminated. A three-dimensional distance image can therefore be calculated from the charges stored in the individual pixels of the CMOS sensor.